1. Field of the Invention
This invention relates generally to the wide area of orthopacdic surgery and traumatology and, more particularly, to the operative treatment of fractures of long bones in humans and animals.
2. Description of Related Art
Many different implants are used internationally and in different parts of the world. Among them are different bone screws (cortical, cancellous, malleolar, DHS, DCS etc.), bone plates (straight, angular etc), different types of external fixators and different intramedullary implants (Kuntcher nail, Rush nail, Ender nail, Kirschner wires implanted intramedullary, xe2x80x9cgama nailxe2x80x9d and, more recently, the interlocking nail). The axial intramedullary screw (AIMS), in accordance with the subject invention and described hereinafter, includes most of the operative indications for all formerly mentioned bone implants (fasteners), and may be used instead of them.
It is logical to compare the axial intramedullary screw (AIMS) with other intramedullary implants (Kuntscher nail, interlocking nail etc. for the osteosynthesis of long bones (humerus, radius, ulna, femur, tibia, fibular, and also metacarpal and metatarsal bones and clavicle). The long bones are emphasized here because fastening two or more bone parts with a single small screw is in wide use. For instance the xe2x80x9cHerbert screwxe2x80x9d (U.S. Pat. No. 4,175,555) is applied to the small scaphoid bone of the hand, which is composed mainly of cancellous (spongy) bone with little diaphyseal part (without tubular cortical part). Therefore, it is the mechanical principle of osteosynthesis of AIMS which is different. The latter is two-sided, which is not the case with the Herbert screw. The same comment may be mentioned for the differences with Huebner screw (WO 94/16636) with variable pitch, applied also for small cancellous bones. The same comment is also true for the compressional screw (WO 94/20040) which compresses the separated bone pieces (not long bone parts to one unit), and it is not applied intramedullary like the Kuntscher nail. In addition, they are all too small, with sizes like standardized (ISO) cortical or cancellous bone screws, for use in fixation of long bones. The current method of treatment of fractures of long bones by intramedullary fixation (Kuntscher nail, interlocking nail etc.) is based on two mechanical principles, gliding and locking. AIMS is more compatible with use for these implants from the point of size, principles of implantation and operative indications. But there is also some differences in basic mechanical principles:
1. Glidingxe2x80x94fragments of the fractured bone are allowed to glide along the implant (Kuntscher nail, Ender and Rush nail) because the friction between the nail and bone is generally small. One form is described in patent application (HR P921004A A2). It is based on the combination of the classical interlocking intramedullary nail and flexible leading screw positioned in the central internal part of the nail. The thread of the central leading screw is smaller than the smaller diameter of the cortical bone and it is in contact with the intramedullary nail. This flexible screw is not in contact with cortical bone (the main mechanical principle of AIMS) and it is not responsible for stability of bone fragments. Also the purpose of this device is distraction (elongation) of the femur and these characteristics are very different from AIMS.
2. Lockingxe2x80x94with transverse screws in multi fragmented diaphyseal fractures. There are three functions for this:
(a) Attainment of axial and rotator stability (interlocking Kuntscher nail, Verrigelungs Nagel);
(b) Possible compression by transverse screw over central intramedullary nail. The best example is the xe2x80x9cgama nailxe2x80x9d described in different variations in many patent applications. For instance in EPO 0 441 577 A3 by the name xe2x80x9cIntramedullary hip screwxe2x80x9d and also in EPO 0 321 170 B1, where term xe2x80x9cintramedullary screwxe2x80x9d is related to transverse spongeosal screw through the femoral neck with the purpose of compression of the femoral head to a central femoral nail (short Kuntscher nail). These two characteristics are very different from the hereafter described variations of the interlocking AIMS.
(c) Modular intramedullary nail (WO 96/02202) is composed 2 or 3 parts (nails) connected with conical connections, but it is different from the modular AIMS hereafter described because it is only a nail and not an intramedullary screw.
The purpose of the AIMS bone implant system in accordance with the subject invention, from the technical point of view, is the same as for other osteosynthetic devices.
It is the object of the present invention, therefore, to maintain relative stability between the fractured bone parts with the purpose of creating optimal conditions for bone healing. During the procedure of application of any osteosynthetic device some basic mechanical principles are used to promote optimal osteosynthesis: namely, (1) Interfragmentary compression (statical and dynamic) by lag screw, plate, external fixator etc.; (2) Gliding (by Kutscher, Rush and Endernail); (3) A combination of the last two principlesxe2x80x94for example compression lag screw and neutralization plates; and, (4) Neutralisation, unloading (neutral support without compression or distraction)xe2x80x94used in the application of interlocking nails in multi fragmented fractures.
The AIMS system may be applied by the use of all the aforementioned mechanical principles depending on the type of fracture or local biomechanical needs.
In one aspect of the invention, there is provided an axial intramedullary screw having a straight cylindrical outer surface for the operative treatment of long bones, the screw having two tips and a screw thread extending between the tips. At each of the tips there is a connection portion for a screwdriver. The screw thread is used for cutting into the cortical bone of the medullary canal and due to the screwdriver connection at both ends it can be driven from either end through the cortical bone. This allows a method to be used in which the screw is threaded into one portion of a bone fragment and then after connecting a further bone fragment at the fracture site, screwed in a different direction into that further fragment.
In another aspect of the invention, the screw also includes a transverse screw hole at one or both ends for the passage of an interlocking transverse screw therethrough.